1. Field of the Invention
The invention relates to a flat shaft of a hip-joint prosthesis for anchoring in the femur according to the precharacterizing clause of claim 1.
2. Description of the Related Art
A shaft of this kind is known from the patent EP 0 032 165 B1. In this known construction the shaft is approximately conically tapered, expanding on all sides from the distal end toward the proximal end, into a region situated at about ⅔ and ¾ of the length of the shaft as measured on its long axis. On the medial narrow side, the conical part of the shaft merges with a continuously curving arch that ends in a collar-like projection. This projection separates a femur-anchoring section of the shaft from a prosthesis neck comprising a peg that tapers conically towards its proximal end, which serves to receive a spherical joint head. The axis of the prosthesis neck intersects the long axis of the shaft at an angle that corresponds substantially to the angle between the neck and axis of the femur in a natural hip joint.
The known construction has proved valuable in that it avoids a so-called “closure rotation” that occurs when the prosthesis is inserted, and does not require the plane of resection to be positioned too low on the neck of the femur. This disadvantagous “closure rotation” is brought about as follows: the blade of the conventional prosthesis shafts must have a certain minimal thickness, so that when such a shaft is completely inserted, it often rotates within the femoral bone because the multiple curvatures of the proximal end of the femur cause a straight or even slightly curved object to be deflected by the wall of the bone.